Apparatus for monitoring loading of a lift

ABSTRACT

A load lift comprising a lifter and a linkage on the lifter carrying a load support for movement therewith to different elevations. The linkage is a four-member linkage which includes a first vertical side member carried by the lifter, a second vertical side member carrying the load support, a third member constituting an upper member of the linkage pivotally connected to the first and second members, and a fourth member constituting a lower member of the linkage pivotally connected to the first and second members. An interconnection between the first and second members holds up the second member and load support and is thereby subject to loading on account of the load support and load thereon. Instrumentation senses the loading on the linkage indicative of the load on the load support.

BACKGROUND OF THE INVENTION

[0001] This invention relates to apparatus for monitoring the loading ofa lift, such as the loading of the work platform of an aerial workplatform lift, and the loading of a forklift; and more particularly forsensing the load on the work platform of the aerial work platform liftor the tines of the forklift.

[0002] As to the monitoring of the loading of the work platform of anaerial work platform lift, reference may be made to U.S. Pat. No.5,913,379 of Paul E. Young and David P. Engvall issued Jun. 22, 1999entitled Articulated Aerial Work Platform System for a disclosure of thetype of aerial work platform lift in which the monitoring apparatus or“load sensor mounting” apparatus of this invention is incorporated, withthe understanding that the apparatus of the invention may beincorporated generally in aerial work platform lifts other than thatshown in said U.S. Pat. No. 5,913,379, which is incorporated herein byreference. A problem which has existed with regard to such lifts hasbeen that of detecting overloading (i.e. excessive weight) on the workplatform of the lift, so that unsafe conditions due to overloading maybe avoided. Excessive weight may be due to the weight of the workman (orworkmen) standing on the work platform plus equipment and items beingused, additive to the weight of the work platform itself. Attempts tosolve this problem have been made; see, for example such prior U.S. Pat.No. 3,952,879 issued Apr. 27, 1976 entitled Overload Control for LiftingBoom and U.S. Pat. No. 4,456,093 issued Jun. 26, 1984 entitled ControlSystem for Aerial Work Platform Machine and Method of Controlling anAerial Work Platform Machine. Other attempts have involved the use ofmultiple load sensors at various locations on the work platform.However, these systems are expensive and not particularly accurate. Thisinvention is regarded as representing an improvement over such systemsand what is disclosed in such prior U.S. patents.

[0003] In addition to being applicable to monitoring the loading of thework platform of an aerial work platform lift, the invention is alsoapplicable to the monitoring of the loading of other lifts, inparticular a forklift, and especially a type of forklift referred to asa rough terrain forklift, such as used on construction sites to liftconstruction materials, for example. In such usage, the forklift mayencounter the problem of a load being picked up on the tines of theforklift in a way as to result in a dangerous situation which, if notremedied, may cause the forklift to tip over. An adjunct of theinvention involves detection of a potential tip-over condition.

[0004] Reference may also be made to the following U.S. Patents as ofinterest re the forklift application of the invention and re otherpotential applications thereof: Pat. No. Date Title 3,724,679 April 3,1973 Indicator or Control for Cranes 4,068,773 Jan. 17, 1978 LiftVehicle with Fail- Safe Overload Protection System 4,093,091 June 6,1978 Load Movement Sensing System for Lift Trucks 5,557,526 Sep. 17,1996 Load Monitoring System for Booms

[0005] In general, a load lift of this invention comprises a lifter(e.g. the boom of an aerial work platform lift, the lifter of aforklift, or the like) and a linkage on the lifter carrying a loadsupport (e.g. the aerial work platform, the tines of the forklift, orthe like) for movement therewith to different elevations. The linkagecomprises a first member carried by the lifter, a second member carryingthe load support, said first and second members constituting sidemembers of the linkage extending generally vertically, a third memberconstituting an upper member of the linkage pivotally connected to thefirst and second members, and a fourth member constituting a lowermember of the linkage pivotally connected to the first and secondmembers. An interconnection between said first and second members holdsup said second member and load support. Instrumentation is provided forsensing the load on the load support.

[0006] This invention is also directed to a load sensor mounting per se(a unit for incorporation in a lift). The mounting generally comprisesthe linkage and instrumentation described above.

[0007] Other objects and features will be in part apparent and in partpointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a view in perspective showing the extensible boom andwork platform of an aerial work platform lift incorporating the loadsensor mounting of this invention, the boom being shown in alongitudinally extended upwardly angled position;

[0009]FIG. 2. is a side elevation of the boom work platform and loadsensor mounting of FIG. 1, the boom being shown in a retracted conditionand in a downwardly angled position;

[0010]FIG. 3 is a view in elevation of one side of the load sensormounting per se, the other side being a mirror image thereof;

[0011]FIG. 4 is a view in elevation of one face of the load sensormounting, the other face appearing the same;

[0012]FIG. 5 is a top plan view of the load sensor mounting;

[0013]FIG. 6 is a bottom view of the load sensor mounting;

[0014]FIG. 7 is a vertical section taken generally on line 7-7 of FIGS.4 and 5 showing in phantom certain framework on the end of the boom (towhich one side of the load sensor mounting is fastened) and also showingin phantom the work platform (which is fastened to the other side of theload sensor mounting);

[0015]FIG. 8 is an exploded view of the load sensor mounting per se inperspective;

[0016]FIG. 9 is a view, partly broken away, of a load cell per se of themounting;

[0017]FIG. 10 is a view of a shear-sensing pin which may be used in theload sensor mounting;

[0018]FIG. 11 is an enlarged fragment of FIG. 10;

[0019]FIG. 12 is a cross-section generally on line 12-12 of FIG. 11;

[0020]FIG. 13 is a fragmentary elevation illustrating the mounting ofthe FIG. 10 pin;

[0021]FIG. 14 is generally an end view of FIG. 13;

[0022]FIG. 15 is a view of a modification of the FIG. 10 pin used in amodification of the mounting of FIGS. 1-8;

[0023]FIG. 16 is an enlarged fragment of FIG. 15; and

[0024]FIG. 17 is a cross-section generally on line 17-17 of FIG. 16.

[0025] Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0026] Referring first to FIGS. 1 and 2 of the drawings, there isgenerally indicated at 1 the boom of an aerial work platform lift suchas disclosed in the aforesaid U.S. Pat. No. 5,913,379, for example, theboom constituting in a broad sense a lifter for the load supportconstituted by the work platform, the latter being identified in itsentirety by the reference numeral 3. The boom 1 and work platform 3 areconventional, the boom being shown as the conventionally telescopicallyextensible boom comprising base section 5, mid-section 7 and tip or end9. The end 9 of the boom includes a framework 11 (e.g., a rotationbracket assembly) carried by leveling apparatus 13 including a hydrauliccylinder 15 for pivotal movement of the framework 11 about a generallyvertical axis indicated generally at A—A and for further pivotalmovement with apparatus 13 about a generally horizontal axis 17 formaintaining the framework 11 in a position for keeping the work platform3 level as the boom 1 pivots up and down and for enabling the workplatform to be pivoted from side-to-side on axis 17. All this isstandard and well-known at this time; reference may be made to said U.S.Pat. No. 5,913,379 for details. The invention resides in means mountingthe work platform 3 on the end of the boom; which means may be referredto as noted as the “load sensor mounting” for the work platform, andwhich is referred to in its entirety by the reference numeral 19. Asshown in FIG. 2, means 19 mounts the work platform 3 on the framework11, but it will be understood that framework 11 could be eliminated andmeans 19 used to mount the work platform directly on the levelingapparatus 13.

[0027] In general, the load sensor mounting 19 comprises a linkage,generally designated 20, which includes a first member 21 carried by theframework 11 on the end of the boom 1 (the lifter), a second member 23carrying the work platform 3 (the load support), said members 21 and 23constituting side members of the linkage, and third and fourth members25 and 27 constituting upper and lower members of the linkage. Thestated first and second members extend generally vertically in closeproximity one to the other, member 21 having upper and lower ends 21 a,21 b, and member 23 having upper and lower ends 23 a, 23 b. The third(upper) member 25 is pivotally connected to the first and second members21 and 23 adjacent their upper ends as indicated at 29 and 31 (FIG. 5)and the fourth member is pivotally connected to the first and secondmembers 21 and 23 adjacent their lower ends as indicated at 33 and 35(FIG. 6). At 37 (FIG. 4) is indicated in its entirety an interconnectionbetween the first and second members 21 and 23 functioning to hold upsaid second member 23 and the work platform 3 (the load support), theinterconnection 37 thereby being subject to loading on account ofholding up the work platform (the load support) and the load thereon. Aswill be described in detail later, instrumentation is provided forsensing the load on the linkage 20 indicative of the loading on the workplatform 3.

[0028] In the preferred embodiment, the side member 21 of the loadsensor mounting 19 comprises an elongate metal bracket generally ofchannel shape in transverse (horizontal) cross- section, thereby havinga web 39 and flanges 41 and 43 extending at right angles to the web(FIG. 8). The web has openings indicated at 45 and 47 and holes 49 forreception of fasteners such as indicated at 50 (see FIG. 7) forfastening it in position extending vertically on the framework 11. Theflanges 41 and 43 have notches indicated at 51 and 53 (FIG. 8) generallymidway of the length (height) thereof, the notch 51 having upper andlower horizontal edges 51 a, 51 b and the notch 53 having upper andlower horizontal edges 53 a, 53 b. Adjacent the upper end 21 a of thebracket 21, its flanges 41, 43 have holes 55 and 57 in transversealignment for reception of a pin 59 a for establishing the pivotalconnection 29. Adjacent the lower end 21 b of bracket 21 its flanges 41,43 have holes 61 and 63 in transverse alignment for reception of a pin59 b for establishing the pivotal connection 33.

[0029] The side member 23 of the load sensor mounting 19 also comprisesan elongate metal bracket generally of channel shape in transverse(horizontal) cross-section, thereby having a web 69 and flanges 71 and73 extending at right angles to the web (FIG. 8). The web has openingsindicated at 75 and 77 and holes 79 for reception of fasteners such asshown at 50 for fastening it in position extending vertically on thework platform 3. The flanges 71 and 73 have noses indicated at 81 and 83generally midway of the length (height) thereof, the nose 81 havingupper and lower horizontal edges 81 a, 81 b and the nose 83 having upperand lower horizontal edges 83 a, 83 b. Adjacent the upper end of thebracket 23, its flanges 71, 73 have holes 85 and 87 in transversealignment for reception of a pin 89 a for establishing the pivotalconnection 29. Adjacent the lower end of bracket 23 its flanges 71, 73have holes 91 and 93 in transverse alignment for reception of a pin 89 bfor establishing the pivotal connection 35.

[0030] The aforesaid third (upper) member 25, which constitutes a linklinking the work platform bracket 23 and the bracket 21 adjacent theupper ends of the brackets comprises a sleeve or tube 95 having a pairof eyes thereon each designated 97 spaced lengthwise thereof on an axisparallel to the axis of the sleeve. The sleeve and eyes are of suitablemetal, each eye being welded to the sleeve by welding, as indicated at25 w (FIG. 5), the effective length of the upper member or link 25 (thedistance between the axis of the eyes 97 and the axis of the sleeve 95),being short in relation to the height of the brackets 21, 23 and thevertical distance between the axes of the pins 59 a, 59 b and 89 a, 89b. The sleeve and eyes could be made integral instead of being weldedtogether. Each pin 59 a, 59 b, 89 a, 89 b is retained in the respectivepin holes by means of C- clips 99 snapped into annular grooves in thepins adjacent their ends.

[0031] The aforesaid fourth (lower) member 27, which constitutes a linklinking the work platform bracket 23 to the bracket 21 adjacent thelower ends of the brackets, like link 25 comprises a sleeve or tube 105having a pair of eyes thereon each designated 107 spaced lengthwisethereof on an axis parallel to the axis of the sleeve. Here again, thesleeve and eyes are of suitable metal, each eye being welded to thesleeve by welding, as indicated at 27 w (FIG. 6), the effective lengthof the upper member or link 27 (the distance between the axis of theeyes 107 and the axis of the sleeve 105), being short in relation to theheight of the brackets 21, 23 and the vertical distance between the axesof the pins 59 a, 59 b and 89 a, 89 b. Here again, the sleeve 105 andeyes 107 could be made integral instead of being welded together.

[0032] The upper link 25 has its eyes 97 pivotally encircling the pin 59a at the upper end of bracket 21 and its sleeve 95 pivotally encirclingthe pin 89 a at the upper end of bracket 23. The lower link 27 has itseyes 107 pivotally encircling the pin 89 b at the lower end of bracket23 and its sleeve 105 pivotally encircling the pin 59 b at the lower endof bracket 21. The arrangement is such as to permit some degree of upand down movement (essentially vertical movement) of bracket 23 relativeto bracket 21 in the direction of the length of bracket 23. Since theupper and lower links 25 and 27 are identical (and of the same effectivelength), permitted movement of bracket 23 is generally vertical in thedirection of its length and parallel to bracket 21. The effective lengthof each of the upper and lower links 25, 27 (which is relatively short)is such that bracket 23 is disposed in close proximity to bracket 21with the edges of the flanges 71, 73 of bracket 23 close to the edges offlanges 51, 53 of bracket 21 and with the noses 81, 83 on flanges 71, 73extending into the notches 51, 53 in flanges 51, 53.

[0033] Suitable bushings (139 in FIG. 13) are provided in sleeves 95,105 and in eyes 97, 107 to insure smooth rotation of these membersrelative to pins 89 a, 89 b, 59 a, 59 b. The bushings may beself-lubricating bushings, bronze bushings or other types of suitablebushings. Roller bearings may also be used.

[0034] Referring to FIGS. 7 and 8, the interconnection 37 is atension-taking interconnection pivotally connected at one endconstituting its upper end to the boom end bracket 21 and at its otherand lower end to the work platform bracket 23. Preferably, thetension-taking interconnection comprises a commercially availableelongate tension load cell 109, more particularly a Model ST-F tensionload cell sold by Strainsert, Union Hill Industrial Park, WestConshohocken, Pa., 19428. For a work platform weighing generally from100 to 200 lbs. which is to carry safely loads up to 500 lbs. TheStrainsert Model ST-F load cell is one comprising a ⅜ inch diameter 16NC 6½ inch long rod (capable of safely carrying at least 4500 lbs.)having load-sensing instrumentation comprising a strain gauge 111 (FIG.9) incorporated therein at the inner end of an axial bore 113 extendingfrom one end thereof (the upper end as illustrated). The load cell 109is generally similar to the force sensing stud disclosed in U.S. Pat.No. 2,873,341 issued Feb. 10, 1959 entitled Electric Strain Gauge andResistance Units Therefor except for having eyes 115 threaded on eachend. The strain gauge is connected in an electrical circuit, wiringthereof being indicated at 117, and acts to provide an electrical outputsignal via the wiring representative of the strain to which the loadcell is subjected and thus serving as a measure of the weight of thework platform 3 and load carried thereby, and utilized for detecting theload on the work platform (e.g. loading thereof totaling more than 500lbs.). The wiring extends from the upper end of the load cell throughthe opening 47 in bracket 21.

[0035] The upper eye 115 is hooked on a hook 119 extending down from asleeve 121 (a short metal tube) pivotally mounted on pin 59 a betweenthe eyes 97 of the upper link 25, and the lower eye 115 is hooked on ahook 123 extending up from a similar sleeve 125 pivotally mounted on pin89 b between the eyes 107 of the lower link 27. Thus, theinterconnection 37 of linkage 20 may generally be considered ascomprising (in order from the top of the mounting 19 down as viewed inFIG. 8) sleeve 121 on pin 59 a, upper hook 119, upper eye 115, load cell109, lower eye 115, lower hook 123, sleeve 125 and pin 89 b. In theabsence of a load on the work platform, the interconnection holds thebracket 23 carrying the work platform in the position wherein the upperedges 81 a, 83 a of the noses 81 and 83 on flanges 71 and 73 of thebracket 23 are slightly (e.g. 0.13 inch) spaced down from the upperedges 51 a and 53 a of notches 51 and 53 and the lower edges 81 b and 83b of the noses 81, 83 and are spaced a somewhat greater but still smalldistance (e.g. 0.25 inch) up from the lower edges 51 b and 53 b of thenotches. Said edges act as interengageable stops (on brackets 21 and 23)limiting the up and down movement of bracket 23 relative to bracket 21.

[0036] The load cell 109 of interconnection 37 continuously monitors theloading of the work platform 3, being stressed and strained in tensionaccording to the weight of the platform and the loading which theplatform is subject to (e.g. the weight of a workman or workmen on theplatform plus items thereon and dynamic forces), acting to transmitelectrical current via wiring 117 depending in value on the strain inthe load cell and thus depending in value on the loading. Overloading,for example, loading in excess of 700 lbs. static load (200 lbs.platform weight) results in the current being of overload-detectingvalue, thereupon acting via suitable and well-known means to trigger anaudible overload alarm, such as a siren, or a visual alarm, such as ared light, or to effect movement of the work platform to a safeposition. An alternative is to have the load cell output interfaced witha computer acting to trigger the alarm or to effect movement of the workplatform to a safe position if the load cell detects an overloadcondition more than a predetermined portion of a predetermined period oftime (e.g. 50% of such period). The latter mode may be preferred onaccount of the platform being subject to dynamic load exceeding whateverstatic load is set as the overload (e.g. 700 lbs. including platformweight of 200 lbs.).

[0037] With the effective length of each of links 25 and 27 short inrelation to the distance between the axes of pins 59 a, 59 b (and thedistance between the axes of pins 89 a, 89 b), preferably less than 50%of that distance, and more preferably less than 25% and most preferablyless than 15% (e.g., 12.5%), the load cell 109 is inclined off verticalonly a small angle and accurately reflects the loading. Thus, thetension on the load cell is generally equal to the loading divided bythe cosine of the angle off vertical, e.g. for an angle of 5° offvertical for the load cell, the tension thereon is the load divided by0.996. The mounting 19 is sufficiently rigid to forces tending to twistthe boom about its axis (e.g., forces resulting from a person movingfrom side to side on the work platform) that the load cell 109 is notaffected by such forces and essentially does not react to them.

[0038] It will be observed from the foregoing that links 21, 23, 25 and27 form a parallelogram linkage, with the upper and lower links beingshort compared to the side links 25 and 27. It will be understood thatother four-member linkages may also be used to practice the presentinvention, and that the lengths of the respective links may vary. Forexample, the upper and lower links may be substantially longer thanlinks 21 and 23 as shown in the drawings. Also, the construction of thelinks may vary from that shown. Further, the construction of theinterconnection 37 may also vary. For example, the load cell 109, eyes115, hooks 119, 123 and sleeves 121, 125 could be formed as an integralmember machined from a piece of suitable metal. Instrumentation otherthan strain gage 111 could also be used for sensing the tension load inthe linkage 20.

[0039] As an adjunct to the above, the load sensor mounting 19 may bemodified to detect not only a vertical load on the load support 3 butalso an overhung load on the load support. This modification hasparticular (albeit not exclusive) application to forklifts, such as arough terrain forklift, where loads substantially overhanging the tinesof the forklift may create large moment forces tending to tip theforklift. In these circumstances, it is desirable to measure such forcesto prevent tipping. As illustrated in FIGS. 10-14, the interconnection37 of the load sensor mounting 19 is modified so that the pin 59 a ofthe bracket 23 is instrumented to measure the shearing force thereon.(This shear force is indicative of the tension in the upper member 25and thus the magnitude of the overhung load). The pin used in place of59 a, designated 59 c in FIGS. 10-14, has strain gauges 131 incorporatedtherein connected in an electrical circuit the wiring of which isindicated at 133 extending out of one end of the pin through an axialbore 135 in the pin. In the event the strain gages 131 sense a shearforce indicative of an overhung load which exceeds a predeterminedmaximum load, an alarm or lift shut-off is triggered.

[0040] As shown in FIG. 12, the preferred embodiment includes fourstrain gages 131, two at each end of the pin 59 c arranged ondiametrically opposite upper and lower sides of the pin on a neutralvertical axis Al of bending moment. These strain gages measure thehorizontal force component of a shear force F exerted on the pin at anangle ω (FIG. 12). This force component (F cos ω) is representative ofthe moment or “overhung” load on the load support 3. The pin 59 c has acircumferential groove 137 adjacent each of its ends at the location ofthe strain gages 131 to provide a reduced pin cross-section for sensingthe shear forces with greater accuracy. It is important that thesegrooves 137 (and the associated strain gages 131) be located atpositions where the shear load is greatest, such as the locations shownin FIG. 13 where the ends of the eyes 97 (and bushings 139 therein) arecentered widthwise of the grooves. The pin is held in this position by akeeper plate 141 fastened to a flange 41 of side member 21 of the loadsensor mounting 19. An edge of the keeper plate 141 is received in aslot 143 in the pin 59 c. The opposite end of the pin has an enlargedhead 145 which engages flange 43 of the side member 21, the end resultbeing that the pin is held in fixed axial position in which the ends ofthe eyes 97 and/or bushings 139 are generally in registry with thegrooves 137 in the pin. The keeper plate 141 also holds in the pin 59 cin a predetermined angular position in which the neutral axis Al ofbending moment is generally vertical to provide an accurate referencefrom which to quantify the output signals of the strain gages 131. (Whenthe strain gages are positioned on a neutral axis which is vertical, thestrain gages will sense only the horizontal component (F cos ω) of shearforce on the pin, which is the component representative of the overhungload; the strain gages will not sense the vertical component (F sin ω)of the force F. An instrumented pin suitable for use is commerciallyavailable from Strainsert, Union Hill Industrial Park, WestConshohocken, Pennsylvania, 19428.

[0041] FIGS. 15-17 illustrate an alternative embodiment capable ofmeasuring both the weight of the load on the platform and the “overhung”load, but without the need to use a tension load cell 109. In thisembodiment, pin 59 c is replaced by an instrumented pin 59 d which issimilar to pin 59 c except that there are two pairs of strain gages ateach end of the pin, a pair of upper and lower strain gages 125 a formeasuring the horizontal component (F cos ω) of any shear force on thepin, indicative of the overhung load, and a pair of left and rightstrain gages 125 b for measuring the vertical component (F sin ω) of anysuch shear force indicative of the weight of the load on the loadsupport 3. The upper and lower strain gages 125 a are located on avertical neutral axis Al of bending moment, and the left and rightstrain gages 125 b are located on a horizontal neutral axis A2 ofbending moment. In this embodiment the load cell 109 is replaced by asimple structural member which functions solely to support the load ofthe platform. An instrumented pin 59 d of suitable manufacture may beobtained from the aforementioned Strainsert company.

[0042] It will be understood that the interconnection 37 between thefirst and second members 21, 23 described can have configurations otherthan those described above without departing from the scope of thisinvention, which is intended to cover any type of linkageinterconnection between the first and second members 21, 23 instrumentedfor sensing the load on the work platform 3 (i.e., the load support).Further, the instrumentation used for sensing the loads may be differentfrom the strain gage systems described above. For example, theinstrumentation could be a spring system comprising a spring (in lieu ofa tension member such as 109) and a device for measuring the deflectionof the spring under a load on the work platform 3. The measuring devicecould be a dial load indicator, or a linear potentiometer or encoderproviding a digital readout of the load, or a set-point device such as aproximity switch for signaling an alarm or shut-off of the machine inthe event of a predetermined load condition. Another method formeasuring the force in the diagonal would be to use a hydraulic cylinderwith a pressure transducer or pressure switch.

[0043] Regardless of how the load is sensed, the load sensor of thepresent invention can have various outputs, as noted above. For example,the output of the load sensor can be displayed as an analog or digitalreadout of the actual load on the platform, or it can be used to signalan alarm or to shut off the machine if a predetermined load condition ismet.

[0044] The load sensing system represents an improvement over priorsystems. Not only is the system more economical, due in large part tothe fact that only a single bracket and load sensor is used, it is alsoaccurate and capable of measuring various load conditions, including theweight on the work platform and the overhung load.

[0045] In view of the above, it will be seen that the several objects ofthe invention are achieved and other advantageous results attained.

[0046] As various changes could be made in the above constructionswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. A load lift comprising a lifter, a linkage on thelifter carrying a load support for movement therewith to differentelevations, said linkage comprising a first member carried by thelifter, a second member carrying the load support, said first and secondmembers constituting side members of the linkage extending generallyvertically, a third member constituting an upper member of the linkagepivotally connected to the first and second members, a fourth memberconstituting a lower member of the linkage pivotally connected to thefirst and second members, and an interconnection between said first andsecond members holding up said second member and load support, saidlifter further comprising instrumentation for sensing the loading onsaid linkage indicative of the loading on said load support.
 2. A loadlift as set forth in claim 1 wherein said interconnection is atension-taking interconnection subject to strain in tension by saidloading.
 3. A load lift as set forth in claim 2 wherein saidinstrumentation is operable for sensing the tension load in saidinterconnection.
 4. A load lift as set forth in claim 3 wherein theinterconnection comprises a tension member pivotally connected at oneend constituting its upper end with said first member and at its otherend constituting its lower end with said second member, and wherein theinstrumentation is in the tension member.
 5. A load lift as set forth inclaim 1 wherein said instrumentation is operable to sense a horizontalcomponent of shear force indicative of a moment force exerted on theload support.
 6. A load lift as set forth in claim 5 wherein saidinstrumentation is further operable for sensing a vertical component ofshear force indicative of the weight of a load on the load support.
 7. Aload lift as set forth in claim 1 wherein said linkage is generally aparallelogram linkage.
 8. A load lift as set forth in claim 7 whereinsaid interconnection comprises a tension member extending diagonallywith respect to the parallelogram linkage.
 9. A load lift as set forthin claim 8 wherein said tension member is pivotally connected at one endconstituting its upper end with said first member and at its other endconstituting its lower end with said second member, said instrumentationbeing operable for sensing the load in said tension member.
 10. A loadlift as set forth in claim 1 wherein said first member comprises anelongate first bracket attached to the lifter extending generallyvertically and movable up and down with the lifter in the direction ofits length and generally vertically throughout its up and down movement,said second member comprises an elongate bracket attached to the loadsupport extending generally vertically generally parallel to the firstbracket between the first bracket and load platform, said third membercomprising an upper link pivotally connected to said brackets and saidfourth member comprises a lower link pivotally connected to saidbrackets.
 11. A load lift as set forth in claim 10 wherein said upperlink is pivotally connected to said brackets on upper pins mounted onsaid brackets and said lower link is pivotally connected to saidbrackets on lower pins mounted on said brackets.
 12. A load lift as setforth in claim 11 wherein said interconnection comprises a tensionmember connected between an upper pin of the first bracket and a lowerpin of the second bracket.
 13. A load lift as set forth in claim 12wherein said instrumentation is in the tension member.
 14. A load liftas set forth in claim 13 wherein said instrumentation is operable forsensing a component of shear force on at least one of said upper andlower pins, said component being indicative of the loading on the loadsupport.
 15. A load lift as set forth in claim 14 wherein saidinstrumentation is operable to sense a horizontal component of shearforce indicative of a moment force exerted on the load support.
 16. Aload lift as set forth in claim 15 said instrumentation comprises astrain gauge system on at least one of said upper or lower pins on theinterconnection.
 17. A load lift as set forth in claim 11 wherein saidinstrumentation is operable for sensing a horizontal component of shearforce indicative of a moment force exerted on the load support, and alsofor sensing a vertical component of shear force indicative of the weightof a load on the load support.
 18. A load lift as set forth in claim 17said instrumentation comprises a strain gauge system on at least one ofsaid upper or lower pins for sensing said horizontal and verticalcomponents of shear force.
 19. A load lift as set forth in claim 11wherein the upper and lower pins are spaced generally the same distanceand wherein the upper and lower links have generally the same effectivelength so that the linkage constituted by said brackets and links isgenerally a parallelogram linkage.
 20. A load lift as set forth in claim19 wherein the effective length of the upper and lower links is afraction of the distance between the upper and lower pins.
 21. A loadlift as set forth in claim 20 having interengageable stops on thebrackets limiting the up and down movement of the second bracketrelative to the first.
 22. A load lift as set forth in claim 11 whereineach bracket is of channel shape in horizontal cross section having aweb and flanges extending from the web, each of the pins extending on agenerally horizontal axis between the flanges, each upper and lower linkcomprising a sleeve and a pair of eyes spaced lengthwise of the sleeveon an axis parallel to that of the sleeve, the upper link having theeyes thereof on the upper pin of the first bracket and the sleevethereof on the upper pin of the second bracket, the lower link havingthe eyes thereof on the lower pin of the second bracket and the sleevethereof on the lower pin of the first bracket, the load cell having apivotal connection with the upper pin of the first bracket between theeyes of the upper link and a pivotal connection with the lower pin ofthe second bracket between the eyes of the lower link.
 23. An aerialwork platform lift comprising a boom carrying the work platformpivotable to move the work platform to different elevations, said boomhaving an end carrying the work platform for pivotal movement of thework platform about a generally horizontal axis to maintain the workplatform generally level as it is moved up and down by the boom, alinkage on the boom end carrying the work platform, said linkagecomprising a generally vertical first bracket attached to said boom endand movable up and down with the boom in the direction of length of saidfirst bracket, a second bracket attached to the work platform extendinggenerally parallel to the first bracket between the first bracket andwork platform, an upper link pivotally connected to said brackets, alower link pivotally connected to said brackets, an interconnectionbetween the first bracket and the second bracket holding up said secondbracket and work platform, and instrumentation for sensing the loadingon said linkage indicative of the loading on the work platform.
 24. Anaerial work platform lift as set forth in claim 23 wherein saidinterconnection is a tension-taking interconnection subject to strain intension by said loading.
 25. An aerial work platform lift as set forthin claim 24 wherein said instrumentation is operable for sensing thetension load in said interconnection.
 26. An aerial work platform liftas set forth in claim 25 wherein the interconnection comprises a tensionmember pivotally connected at one end constituting its upper end withsaid first member and at its other end constituting its lower end withsaid second member, and wherein the instrumentation is in the tensionmember.
 27. An aerial work platform as set forth in claim 23 whereinsaid instrumentation is operable to sense a horizontal component ofshear force indicative of a moment force exerted on the load support.28. An aerial work platform as set forth in claim 27 wherein saidinstrumentation is further operable for sensing a vertical component ofshear force indicative of the weight of a load on the load support. 29.An aerial work platform lift as set forth in claim 23 wherein saidlinkage is generally a parallelogram linkage.
 30. An aerial workplatform lift as set forth in claim 29 wherein said interconnectioncomprises a tension member extending diagonally with respect to theparallelogram linkage.
 31. An aerial work platform lift as set forth inclaim 30 wherein said tension member is pivotally connected at one endconstituting its upper end with said first member and at its other endconstituting its lower end with said second member, said instrumentationbeing operable for sensing the load in said tension member.
 32. Anaerial work platform lift as set forth in claim 21 wherein said firstmember comprises an elongate first bracket attached to the lifterextending generally vertically and movable up and down with the lifterin the direction of its length and generally vertically throughout itsup and down movement, said second member comprises an elongate bracketattached to the load support extending generally vertically generallyparallel to the first bracket between the first bracket and loadplatform, said third member comprising an upper link pivotally connectedto said brackets and said fourth member comprises a lower link pivotallyconnected to said brackets.
 33. An aerial work platform lift as setforth in claim 32 wherein said upper link is pivotally connected to saidbrackets on upper pins mounted on said brackets and said lower link ispivotally connected to said brackets on lower pins mounted on saidbrackets.
 34. An aerial work platform lift as set forth in claim 33wherein said interconnection comprises a tension member connectedbetween an upper pin of the first bracket and a lower pin of the secondbracket.
 35. An aerial work platform lift as set forth in claim 34wherein said instrumentation is in the tension member.
 36. An aerialwork platform lift as set forth in claim 35 wherein said instrumentationis operable for sensing a component of shear force on at least one ofsaid upper and lower pins, said component being indicative of theloading on the load support.
 37. An aerial work platform lift as setforth in claim 36 wherein said instrumentation is operable to sense ahorizontal component of shear force indicative of a moment force exertedon the load support.
 38. An aerial work platform lift as set forth inclaim 37 said instrumentation comprises a strain gauge system on atleast one of said upper and lower pins.
 39. An aerial work platform liftas set forth in claim 33 wherein said instrumentation is operable forsensing a horizontal component of shear force indicative of a momentforce exerted on the load support, and also for sensing a verticalcomponent of shear force indicative of the weight of a load on the loadsupport.
 40. An aerial work platform lift as set forth in claim 39 saidinstrumentation comprises a strain gauge system on at least one of saidupper and lower pins for sensing said horizontal and vertical componentsof shear force.
 41. An aerial work platform lift as set forth in claim33 wherein the upper and lower pins are spaced generally the samedistance and wherein the upper and lower links have generally the sameeffective length so that the linkage constituted by said brackets andlinks is generally a parallelogram linkage.
 42. An aerial work platformlift as set forth in claim 41 wherein the effective length of the upperand lower links is a fraction of the distance between the upper andlower pins.
 43. An aerial work platform lift as set forth in claim 41having interengageable stops on the brackets limiting the up and downmovement of the second bracket relative to the first.
 44. An aerial workplatform lift as set forth in claim 33 wherein each bracket is ofchannel shape in horizontal cross section having a web and flangesextending from the web, each of the pins extending on a generallyhorizontal axis between the flanges, each upper and lower linkcomprising a sleeve and a pair of eyes spaced lengthwise of the sleeveon an axis parallel to that of the sleeve, the upper link having theeyes thereof on the upper pin of the first bracket and the sleevethereof on the upper pin of the second bracket, the lower link havingthe eyes thereof on the lower pin of the second bracket and the sleevethereof on the lower pin of the first bracket, the load cell having apivotal connection with the upper pin of the first bracket between theeyes of the upper link and a pivotal connection with the lower pin ofthe second bracket between the eyes of the lower link.
 45. A load sensormounting for the load support of a load lift having a lifter, saidmounting comprising a linkage including a first side member forattachment to the lifter in generally vertical position, a second sidemember for attachment to the load support in generally verticalposition, an upper member pivotally connected to the side members, alower member pivotally to the side members, an interconnection betweenthe side members for holding up the second side member and the loadsupport, said mounting further comprising instrumentation for sensingthe loading on said linkage indicative of the load on said load support.46. A load sensor mounting as set forth in claim 45 wherein saidinterconnection is a tension-taking interconnection subject to strain intension by said loading.
 47. A load sensor mounting as set forth inclaim 46 wherein said instrumentation is operable for sensing thetension load in said interconnection.
 48. A load sensor mounting as setforth in claim 47 wherein the interconnection comprises a tension memberpivotally connected at one end constituting its upper end with saidfirst member and at its other end constituting its lower end with saidsecond member, and wherein the instrumentation is in the tension member.49. A load sensor mounting as set forth in claim 45 wherein saidinstrumentation is operable to sense a horizontal component of shearforce indicative of a moment force exerted on the load support.
 50. Aload sensor mounting as set forth in claim 49 wherein saidinstrumentation is further operable for sensing a vertical component ofshear force indicative of the weight of a load on the load support. 51.A load sensor mounting as set forth in claim 45 wherein said linkage isgenerally a parallelogram linkage.
 52. A load sensor mounting as setforth in claim 45 wherein said interconnection comprises a tensionmember extending diagonally with respect to the parallelogram linkage.53. A load sensor mounting as set forth in claim 52 wherein said tensionmember is pivotally connected at one end constituting its upper end withsaid first member and at its other end constituting its lower end withsaid second member, said instrumentation being operable for sensing theload in said tension member.
 54. A load sensor mounting as set forth inclaim 45 wherein said first member comprises an elongate first bracketattached to the lifter extending generally vertically and movable up anddown with the lifter in the direction of its length and generallyvertically throughout its up and down movement, said second membercomprises an elongate bracket attached to the load support extendinggenerally vertically generally parallel to the first bracket between thefirst bracket and load platform, said third member comprising an upperlink pivotally connected to said brackets and said fourth membercomprises a lower link pivotally connected to said brackets.
 55. A loadsensor mounting as set forth in claim 54 wherein said upper link ispivotally connected to said brackets on upper pins mounted on saidbrackets and said lower link is pivotally connected to said brackets onlower pins mounted on said brackets.
 56. A load sensor mounting as setforth in claim 55 wherein said interconnection comprises a tensionmember connected between an upper pin of the first bracket and a lowerpin of the second bracket.
 57. A load sensor mounting as set forth inclaim 56 wherein said instrumentation is in the tension member.
 58. Aload sensor mounting as set forth in claim 57 wherein saidinstrumentation is operable for sensing a component of shear force on atleast one of said upper and lower pins, said component being indicativeof the loading on the load support.
 59. A load sensor mounting as setforth in claim 58 wherein said instrumentation is operable to sense ahorizontal component of shear force indicative of a moment force exertedon the load support.
 60. A load sensor mounting as set forth in claim 59said instrumentation comprises a strain gauge system on at least one ofsaid upper and lower pins.
 61. A load sensor mounting as set forth inclaim 55 wherein said instrumentation is operable for sensing ahorizontal component of shear force indicative of a moment force exertedon the load support, and also for sensing a vertical component of shearforce indicative of the weight of a load on the load support.
 62. A loadsensor mounting as set forth in claim 61 said instrumentation comprisesa strain gauge system on at least one of said upper or lower pins forsensing said horizontal and vertical components of shear force.
 63. Aload sensor mounting as set forth in claim 55 wherein the upper andlower pins are spaced generally the same distance and wherein the upperand lower links have generally the same effective length so that thelinkage constituted by said brackets and links is generally aparallelogram linkage.
 64. A load sensor mounting as set forth in claim63 wherein the effective length of the upper and lower links is afraction of the distance between the upper and lower pins.
 65. A loadsensor mounting as set forth in claim 64 having interengageable stops onthe brackets limiting the up and down movement of the second bracketrelative to the first.
 66. A load sensor mounting as set forth in claim55 wherein each bracket is of channel shape in horizontal cross sectionhaving a web and flanges extending from the web, each of the pinsextending on a generally horizontal axis between the flanges, each upperand lower link comprising a sleeve and a pair of eyes spaced lengthwiseof the sleeve on an axis parallel to that of the sleeve, the upper linkhaving the eyes thereof on the upper pin of the first bracket and thesleeve thereof on the upper pin of the second bracket, the lower linkhaving the eyes thereof on the lower pin of the second bracket and thesleeve thereof on the lower pin of the first bracket, the load cellhaving a pivotal connection with the upper pin of the first bracketbetween the eyes of the upper link and a pivotal connection with thelower pin of the second bracket between the eyes of the lower link.